Especially in ring-spinning machines and ring-twisting machines in which the yarn or thread arrives from a drafting frame, passes through a traveller orbiting on a ring around a spindle and winds the yarn or thread in a yarn package or bobbin on a core sleeve or tube on the spindle, and an automatic bobbin change mechanism is provided for removing a fully wound bobbin from the spindle and replacing it with an empty core sleeve, it has been desirable to wind the tail thread, i.e. the thread length or yarn length coming from the traveller following the last bobbin winding, on the spindle below the bobbin.
As soon as the ring-spinning or ring-twisting operation is complete and the bobbin fully wound, the spinning is usually terminated and a cover thread or yarn, a reserve thread or yarn and an unwinding can be formed. The formation of the underwinding in a number of turns below the underwinding crown in a milled or knurled region of the whorl of the spindle is common.
As a result, a number of turns of thread accumulate on the knurled or milled region since, with the doffing of each full bobbin, the unwinding thread is broken away from the bobbin thread and remains on the spindle after the new core tube is mounted and winding of a bobbin is begun again.
In automatically doffing systems of this type, it has been necessary from time to time to remove the turns of the underwinding thread which have accumulated and this can be achieved by manually operating a device for removing the underwinding (see German Patent Document DE 29 31 209) or through the use of an automatic cleaning element (see German Patent Document G 91 11 455.1).
The removal of the accumulated underwindings must be carried out in conjunction with evacuation of the lint and underwinding thread particles which are cut away to avoid the entrapment of the line or yarn particles in the yarn which is being wound up on the same station or at the other spindle stations of the ring spinning or ring twisting machine.
Systems involve evacuation of lint, dust and scraps of yarn and collecting these materials as they are drawn off by suction have high capital cost and take up considerable space on the machine. This is also true for the device or devices which actually cut away the turns of the underwinding which have accumulated.
In recent years systems have been developed which avoid these disadvantages by minimizing the amount of underwinding that can accumulate on a spindle or by eliminating the accumulation of underwindings altogether.
This can be achieved by providing a clamp beneath the bobbin or yarn package which can engage the underwinding thread or yarn so that full turns or multiple turns of an unwinding need not accumulate. When the unwinding is present in a loop of less than 360.degree., for example, the release of the clamp can release the unwinding during the subsequent bobbin winding operation so that there is no accumulation of yarn or thread on the spindle which must be cleared away with the complications enumerated above.
For example, a clamping system for this purpose is described in EP 0 292 856 A1 which relies upon centrifugal force. A clamping gap is opened and in the terminal spinning operations, enables a partial turn of the unwinding to be clamped and later released. To reset the clamping body during the terminal stages of spinning into a clamping position, a restoring element, e.g. an annular spring can be used in another construction (see EP 0 358 032 A1).
An actuating element can operate on an axially shiftable clamping sleeve in EP 0 462 467 B1 which can be moved between working and open positions in a restoring element, for example a spring which acts in a direction parallel to the longitudinal axis of the spindle shaft is here used.
Still another construction utilizing the actuation of a sleeve is described for a ring-spinning or twisting machine in EP 0 587 526 A1 and here the actuating member can provide independent operation of the respective sleeve and is actuatable via a slide arrangement. The sleeves can be operated independently of the parameters of the spinning program, especially the spindle speed, or in dependence upon the spinning program. The restoring member can be a coil spring. Another clamping system is described in EP 0 775 769 A1 for clamping the underwinding thread of a spindle and provides an axially displaceable member on the spindle which can bring a clamping sleeve into engagement with the underwinding thread against a collar of the spindle after the underwinding thread has formed a turn of less than 360.degree.. An actuating device can be fixed on the machine and a unit is provided for holding the clamping sleeve in the clamping position independently of the actuating device.
Finally, mention may be made of the system described in DE 196 288 26 A1 which provides a clamping system for a thread on a spindle on a spinning or twisting machine and which utilizes a fixed clamping element and an axially shiftable clamping element. The shiftable clamping element has a conical inner surface which is engaged by a centrifugal element which is movable independently of the shiftable clamping element.
While these systems have been found to be effective in providing the clamping action previously described, reliability requires improvement and in many systems, the mechanism is excessively complex.